The method of securing the rotor and lid of a centrifuge to the rotating head proposed in patent literature 1 is known as a prior-art method. The centrifuge shown in patent literature 1 comprises a rotating shaft, a rotating head secured to one end of the rotating shaft, a rotor attached to the rotating head, and a lid covering the upper surface of the rotor. The knob shaft is secured to the knob. When the knob is turned to secure the knob shaft to the rotating head, the rotor as well as the lid is secured to the rotating head. Since tightening the lid also secures the rotor, both the lid and the rotor can be easily secured.